Indicas ae simply percieved as being high yielding due to their rapid turnover of bud (and a good bud/leaves ratio)-you can have several harvests a year. Sativas need atleast 8 months to mature fully-what do you think will produce greater yields-an eight foot sativa or a four foot indica?

Check out breeds such as old mother sativa which is often grown in Australia, grows 12 feet tall and yields several pounds of pud-a lot more than a single indica plant ever could.

Indica/sativa hybrids are even better however, producing better yields than either two species alone.